This application is based on Application No. 2001-328890, filed in Japan on Oct. 26, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an abnormality diagnosis apparatus of an internal combustion engine for determining abnormality in a fuel system (e.g., injector(s)) used in a vehicle engine and so on, and more particularly, to such an abnormality diagnosis apparatus of an internal combustion engine which is capable of improving reliability in the abnormality determination as well as making abnormality determination at high frequencies.
2. Description of the Prior Art
In general, in a control system for an internal combustion engine, in order to perform feedback control on the amount of fuel injected from each injector in accordance with the operating condition of the engine, an oxygen sensor is provided on an exhaust pipe for detecting the concentration of oxygen in exhaust gases flowing therethrough so that the amount of fuel to be injected from each injector can be controlled in a feedback manner in accordance with the oxygen concentration thus detected.
In addition, during the operation of the internal combustion engine, it is necessary to diagnose the functionality of the fuel system including the injectors or the oxygen sensor so as to maintain the feedback control on the amount of fuel supplied to the internal combustion engine in a reliable manner.
In these circumstances, there have been conventionally proposed a variety of abnormality diagnosis apparatuses for determining the presence or absence of abnormality in a fuel system or an oxygen sensor in an internal combustion engine.
For instance, as a first prior art example, Japanese Patent Application Laid-Open No. 4-269350 or Japanese Patent Application Laid-Open No. 6-17692 describes an apparatus for determining abnormality in a fuel system for a part of engine cylinders based on the state of an output signal from an oxygen sensor.
However, since in the above-mentioned first prior art example, the feedback condition based on the detection signal of the oxygen sensor is not specified, there would be a fear that when the detection signal of the oxygen sensor is varied by external disturbances (changes in load or in the number of revolutions per minute of the engine, etc.) other than abnormality in the fuel system, it might be determined by mistake that there has taken place abnormality.
Moreover, as a second prior art example, Japanese Patent Application Laid-Open No. 2-11840 describes an apparatus for determining abnormality in an oxygen sensor based on the state of a signal from the oxygen sensor representative of the concentration of oxygen detected in the course of a forced fuel correction control operation.
However, in this second prior art example, abnormality determination for the oxygen sensor is made only during the forced fuel correction control operation, and hence it is impossible to carry out oxygen sensor abnormality determination with high frequencies or highly frequently.
Additionally, as a third prior art example, Japanese Patent Application Laid-Open No. 63-219848 describes an apparatus for determining abnormality in a fuel system by using the amount of fuel controlled in a feedback manner based on a detection signal (oxygen concentration) of an oxygen sensor and the amount of control learned for the feedback-controlled fuel amount.
However, in the third prior art example, it is only possible to detect abnormality in the entire fuel system, but not to detect abnormality in a part of the fuel system for respective engine cylinders.
As described above, the prior art abnormality diagnosis apparatuses have the following problems. That is, in the first prior art example, when the detection signal of the oxygen sensor is disordered by external disturbances other than abnormality in the fuel system, it might mistakenly be determined that the oxygen sensor is abnormal.
In addition, in the second prior art example, it is impossible to detect abnormality in the oxygen sensor with high frequencies or highly frequently.
Moreover, in the third prior art example, it is impossible to detect abnormality in the fuel system for a part of cylinders.
The present invention is intended to obviate the various problems as referred to above, and has for its object to provide an abnormality diagnosis apparatus of an internal combustion engine which is capable of improving reliability in abnormality determination as well as making abnormality determination at high frequencies or highly frequently.
Bearing the above object in mind, according to the present invention, there is provided an abnormality diagnosis apparatus of an internal combustion engine including: an oxygen sensor for detecting a concentration of oxygen in exhaust gases of an internal combustion engine; an injector for injecting fuel into the internal combustion engine; a feedback control element for driving the injector according to the concentration of oxygen to control an amount of fuel supplied to the internal combustion engine in a feedback manner; a forced fuel correction element for correcting an amount of fuel controlled by the feedback control element in a forced manner; and an abnormality determination element for determining the presence or absence of abnormality in the injector. The abnormality determination element determines the presence or absence of abnormality in the injector based on the concentration of oxygen detected by the oxygen sensor in the course of a forced fuel correction control operation carried out by the forced fuel correction element.
In a preferred form of the present invention, the forced fuel correction element carries out the forced fuel correction control on the amount of control fuel when the operating condition of the internal combustion engine is in a stable state.
In another preferred form of the present invention, before determining the presence or absence of abnormality in the injector, the abnormality determination element determines the presence or absence of abnormality in the oxygen sensor based on the concentration of oxygen detected by the oxygen sensor in the course of the forced fuel correction control operation carried out by the forced fuel correction element, and further determines the presence or absence of abnormality in the injector only when the oxygen sensor is not abnormal.
In a further preferred form of the present invention, the abnormality determination element is provided with warning information element and drives the warning information element when it is determined that the oxygen sensor or the injector is abnormal.
In a still further preferred embodiment of the present invention, when the amount of fuel controlled by the feedback control element varies from a reference value by a prescribed value or more, the abnormality determination element determines that the amount of control fuel is abnormal, and further determines that the fuel system including the injector is abnormal when it is determined that at least one of the injector and the amount of control fuel is abnormal.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.